Topical delivery of active compounds is well known. Unfortunately, many topical delivery formulations are not waterproof or water resistant. Thus, when these active agents are applied to the skin and exposed to moisture, most of the active agents are often washed away from the skin thereby reducing their effectiveness.
There are many challenges in the topical application of active agents. For example, application of active agents should be easy and smooth. Moreover, in some instances the composition should remain within the applied area for a prolonged period even when exposed to moisture to provide a relatively constant amount of the active agent within the applied area.
Water resistant or very water resistant formulations of topical delivery systems are especially desirable because they eliminate the need for reapplication after exposure of the applied area to water, such as after swimming, bathing or excessive perspiration. This is particularly true for sunscreen products.
Sunscreen products provide protection for the human skin against damages of ultraviolet light. Products with various sun protection factor (SPF) values are available, thus allowing consumers to choose the amount of protection desired. While a variety of sunscreen products are available, “water resistant” or “very water resistant” sunscreens are especially desirable because they eliminate the need for reapplication after swimming, bathing or excessive perspiration. Generally “water resistant” sunscreen formulations can undergo at least about 40 minutes of water immersion without significant SPF loss, whereas “very water resistant” sunscreen formulations can undergo at least about 80 minutes of water immersion without significant SPF loss.
Ideally, sunscreen products should be stable and easy to apply, and provide acceptable consistency and skin-feel. The foregoing factors, which are important to achieving consistent distribution on the skin, even sun protection, along with consumer acceptance and commercial viability, are largely functions of the vehicle which carries the sunscreen agents.
For the above reasons, it is clearly desirable to formulate a topical vehicle that is capable of providing acceptable consistency, skin feel and stability, and is easy to use and apply sunscreen agents, and, thereby, achieve both water resistant character and high-SPF values. The present invention fulfills such needs.